The connecting rod in an internal combustion engine connects the crankshaft to a piston. The connecting rod has one end including a bore that is configured to attach to the wrist pin a piston, and the connecting rod has an opposing larger end including a bore that is configured to attach to the eccentric pin on a crankshaft. This larger end typically includes a separate bearing cap that in part defines the bore and can be attached to the remaining portion of the connecting rod, so as to mount the pin of the crankshaft within the bore. In the past, the normal practice was to initially mold and machine the connecting rod in two pieces that would then be bolted together on the crankshaft pin.
More recent manufacturing processes separate a bearing cap from a one-piece rod, e.g., by cracking or fracturing the rod. This method typically utilizes an expansion mandrel that applies tension force of relatively great magnitude within the bore and along the longitudinal axis of the connecting rod, thus causing the rod to completely fracture and form the connecting rod and the separate bearing cap. More specifically, the mandrel can include a pair of opposing semi-circular protrusions received within a circular bore formed in the end of the rod. The semi-circular protrusions can be nested against the inner diameter surface of the bore and apply the longitudinal force to separate the bearing cap from rest of the connecting rod. However, known mandrel protrusions apply the load specifically to centrally disposed portions of the inner diameter surface that are disposed along the longitudinal axis of the rod, which can cause the opposing sides of the bearing cap adjacent the fracture to be deformed in a somewhat radially inward direction. Thus, when the connecting rod is assembled and mounted to the crankshaft pin after the cracking process is completed, the bore may be non-circular as a result of the side portions being displaced somewhat radially inward. These sides may bear a larger portion of the load than the remaining portions of the bearing cap and the connecting rod.
Accordingly, there is a need for a method and apparatus configured to crack a connecting rod while maintaining a circular bore shape in the connecting rod.